1. Field of the Invention
The present invention relates to public health and, more particularly, to monitoring a person's exposure to contaminants in the environment and a device for carrying out such monitoring.
2. The Prior Art
Prior techniques for monitoring exposure to environmental contaminants have been frequently limited to conventional sampling and analytical techniques for personal measurement or the use of bulky non-personal devices for determining contaminant concentration in general work environments.
In the case of ammonia, (a common environmental contaminant), current monitoring techniques include the following. NIOSH Method P&CAM 205 (NIOSH Manual of Analytical Methods, Second Ed., Vol. 1, Apr. 1977, NIOSH, CDC, PHS) requires that a sampler containing sulfuric acid be attached to the worker, with a 15 minute time weighted average exposure determined by subsequent laboratory analysis of the sample. NIOSH Method S347 (Ibid, Vol. 5) replaces the liquid acid with a solid sorbent tube, but extends the sampling period to approximately four hours, and still requires post-sampling laboratory analysis. Thus, neither of these methods allow for real-time determination of the safety of the worker.
The use of direct reading instrumental techniques, such as portable infrared analyzers, provide a real-time determination of ammonia concentration in the air, but it is seldom possible to determine the concentration of analyte in a person's breathing zone by this technique. Since this type of analyzer requires 110 VAC power and weighs approximately 50 pounds (depending on the model), it is not possible to follow a worker to various work stations, i.e., the device lacks reasonable portability. Therefore, only in those rare instances where an individual remains in one location is this a possible method for measuring personal exposure to contaminant, and even then there are significant limitations.
While these examples are specific to one environmental contaminant (ammonia), they are typical of the types of sampling required for other contaminants, including mercury, carbon monoxide, and formaldehyde.
A number of patents have been issued on devices which are designed to detect a change in some optical properties as a result of exposure of a sensor to a gas phase material. Thus, U.S. Pat. No. 3,114,610 to Gafford et al discloses a continuous sampling gas analyzer which uses a gel substance which contains a neutral liquid (water) which evaporates and gives the sensing gel a short life; this life is increased to some extent by the inclusion of a semi-permeable membrane, but even then the practical life of the device is limited. Further, this patent only covers gels which will change color due to changes in pH sensitive dye when it reacts with the analyte of interest, thus limiting the scope of use. Gafford's improved version of the device (shown in FIG. 2 of the patent) increases response time but uses two light sources, thus increasing its cost and complexity.
U.S. Pat. No. 3,853,477 to Block et al discloses a device for measuring only ethanol in discrete samples of air, for example breath. Block's device has both an active and reference side in the detector, however both sides use liquid reagent. While smaller in size than many laboratory instruments, its portability is nonetheless limited by its utilization of 110 VAC power.
U.S. Pat. No. 4,484,818 to Houston only covers oxygen detection using a barium metal film. The device also does not have a reference side to the detector, and thus is not nearly as sensitive as is physically possible. It does not measure analyte in the sense that it provides information on the amount present; rather it is an endpoint indicator providing evidence that a predetermined level has been obtained. The scientific principle on which this device is based precludes the possibility of using such a device to measure any analyte in an air matrix.
U.S. Pat. No. 4,513,087 to Giuliani et al covers only oxazine perchlorate reactions in an optical waveguide. Thus it is only sensitive to ammonia, hydrazine or pyridine, and the reaction is reversible (the color of the indicator will return to normal when the concentration of ammonia is zero) and leaves no permanent record of reaction. It also does not use a reference beam to detect and compensate for changes in the light source output.
U.S. No. 4,661,320 to Ito et al is for hydrogen only and specifically only for a detector which uses a "catalytic metal". The scientific principle on which this device is based precludes the possibility of using such a device to measure other analytes in air.
none of these patents provide a device which can monitor, in real time, the amount of contaminants in the environment to which a worker has been exposed.